This invention relates to photographic measurements, and more particularly to a method of obtaining a D(log E) curve for an unknown film.
Photographic analyses frequently require knowledge of the density (D) and relative exposure (E) relationship of a film, more commonly called the D(log E) or H and D curve. The D(log E) relationship is usually obtained by exposing the film through a "step wedge" of known log E steps before processing.
Unfortunately, step wedge data is frequently not available for a roll of film under analysis, and a technique to obtain the D(log E) curve directly from the photographic record would be of great value. The present invention discloses such a technique.
The present invention permits determination of the D(log E) relationship of a film record in the absence of a step wedge. The only film information required is specification of film type, so that an x(log E) relationship for that film can be constructed or recalled from previous work. As a result, the technique will greatly expand the data base for remote sensing programs. It will permit use of a large body of imagery, currently in film libraries, which does not have step wedge information and hence is not usable in photometric analyses. It will also permit use of imagery yet to be collected on which step wedge data may be improperly affixed or omitted.